1. Field of the Invention
The present invention generally relates to a document reading apparatus for reading a document by projecting an image light of the document onto an image sensor, and an image formation apparatus therewith; and especially relates to a document reading apparatus that includes an energy-saving power supply unit, and an image formation apparatus therewith. The document reading apparatus of the present invention can be used by a document scanner, a digital copier, and a facsimile apparatus, among other things.
2. Description of the Related Art
[Patent Reference 1] JPA 2004-229110
[Patent Reference 2] JPA 2004-109639
[Patent Reference 3] JPA 2004-320333.
Patent Reference 1 discloses
an image signal processing circuit for converting an image signal generated by a CCD into digital image data, wherein image data of a reference white plate read by the CCD are adjusted to a proper value, and
output compensation control for updating image signal amplification gain, an offset, a reference voltage of D/A conversion, and the like.
Patent Reference 2 discloses a document reading apparatus wherein
a first carriage of a flat bed is driven to a position of a reference white plate, when shifting from a standby state to a power-saving state, and
the reference white plate is read and the first carriage is driven to a position Ph for reading the document size, when returning from the power-saving state to the standby state.
Patent Reference 3 discloses a copying machine, wherein
an image reading unit acquires the time duration of an energy-saving mode from a printer engine controller when the copying machine returns from the energy-saving mode to the operating mode,
if the duration is greater than a predetermined value, parameters are initialized and stored in a non-volatile memory, the parameters influencing digital conversion characteristics of an image signal processing circuit for carrying out digital conversion of an image signal of a solid state image sensor, such as a CCD, into image data, such that proper image data can be acquired, and
if the elapsed time from the latest initialization is less than a predetermined value, the parameters are obtained from the non-volatile memory, and the read parameters are set in the image signal processing circuit.
Conventionally, when the power is turned on for a document scanner, homing, AGC (Automatic Gain Control), etc., are performed before document size detection. Homing is to initialize vertical scanning position information by using position information of a reference point sensor provided at a predetermined position in the vertical scanning direction, when the reference point sensor (for example, a home position sensor) detects a carriage for carrying out vertical scanning of a document while the carriage is moved in the vertical scanning direction. Output compensation control such as AGC is carried out by
driving the carriage to a position of reading a reference white plate,
reading the reference white plate, and
updating parameters, such as image signal amplification gain, of an image signal processing circuit that digitally converts an image signal from an image sensor, such as CCD, into image data so that proper image data are obtained. The output compensation control turns on a lamp (luminous source), reads a reflected light level of the white reference board, and adjusts the digital conversion parameters, such as the amplification gain, an offset, and a reference voltage of D/A conversion, when carrying out the digital conversion of the read image signal into the image data, so that proper image data can be obtained. This is a relatively time consuming process.
Image processing systems available in recent years and continuing often include a power supply unit with an energy-saving mode. A part or all of power supplied to a document scanner and a printer is automatically interrupted if the system is not used for a time longer than a predetermined time (waiting time), and supplying the power to the document scanner and the printer is automatically resumed in response to a user operation of the image processing system. Here, if the control of output compensation of the document scanner, such as AGC, is to be carried out whenever supplying the power is resumed, it takes time before document reading by the document scanner can be started. In view of this, according to Patent Reference 3, the printer engine controller measures duration of the energy-saving mode, the image reading unit obtains the duration of the energy-saving mode, and output compensation control such as AGC is carried out if the duration is longer than the predetermined time; the image reading unit obtains compensation data from the memory if the duration is shorter than the predetermined time.